Array elements with prime frequencies

Last Updated : 03 Mar, 2023

Given a string. The task is to find the count of characters whose number of occurrences is prime.

Examples:

Input : str = "geeksforgeeks"
Output : 3
Count of occurrences of characters are:
g -> 2
e -> 4
k -> 2
s -> 2
f -> 1
o -> 1
r -> 1
So, g, k and s occurs prime number of times i.e. 2

Input : str = "aabbcc"
Output : 3

Start traversing the string and count the occurrences of each character using a map in C++ and check whether an occurrence is prime or not. If prime then increment the count otherwise not.

Algorithm:

Create a static function named "check_prime" with a boolean return type that takes an integer as the input value.
that will return true or false if the number is prime or not.
Create a static function named countPrimeFreuent with in return type which takes a string as input.
initialize an int variable count with a value of 0
To store the frequency of each character in the string s, create a hashmap called mp.
- start for loop inside function which traverses the input string and updates its frequency in mp
- now iterate the map and characters with prime occurrences, If the frequency is prime, increment the count variable
return the value of the count

Below is the implementation of the above approach:

C++

// C++ program to find count of numbers
// with prime frequencies

#include <bits/stdc++.h>
using namespace std;

// Function to check if a
// number is prime
bool check_prime(int n)
{
    // Corner cases
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;

    // This is checked so that we can skip
    // middle five numbers in below loop
    if (n % 2 == 0 || n % 3 == 0)
        return false;

    for (int i = 5; i * i <= n; i = i + 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return false;

    return true;
}

// Function to find count of numbers
// with prime frequencies
int countPrimeFrequent(string s)
{
    int count = 0;

    // create a map to store
    // frequency of each character
    unordered_map<char, int> mp;

    // Store frequency of each character
    // in the map
    for (int i = 0; i < s.length(); i++)
        mp[s[i]]++;

    // now iterate the map and characters
    // with prime occurrences
    for (auto it = mp.begin(); it != mp.end(); it++) {

        // if prime then increment count
        if (check_prime(it->second))
            count++;
    }

    return count;
}

// Driver Code
int main()
{
    string s = "geeksforgeeks";

    cout << countPrimeFrequent(s);

    return 0;
}

Java

// Java program to find count of numbers
// with prime frequencies

import java.util.*;

class GFG
{

    // Function to check if a
    // number is prime
    static boolean check_prime(int n) 
    {
        // Corner cases
        if (n <= 1)
        {
            return false;
        }
        if (n <= 3)
        {
            return true;
        }

        // This is checked so that we can skip
        // middle five numbers in below loop
        if (n % 2 == 0 || n % 3 == 0)
        {
            return false;
        }

        for (int i = 5; i * i <= n; i = i + 6)
        {
            if (n % i == 0 || n % (i + 2) == 0) 
            {
                return false;
            }
        }

        return true;
    }

    // Function to find count of numbers
    // with prime frequencies
    static int countPrimeFrequent(String s)
    {
        int count = 0;

        // create a map to store
        // frequency of each character
        Map<Character, Integer> mp = new HashMap<>();

        // Store frequency of each character
        // in the map
        for (int i = 0; i < s.length(); i++)
        {
            if (mp.containsKey(s.charAt(i)))
            {
                mp.put(s.charAt(i), mp.get(s.charAt(i)) + 1);
            } 
            else 
            {
                mp.put(s.charAt(i), 1);
            }
        }

        // now iterate the map and characters
        // with prime occurrences
        for (Map.Entry<Character, Integer> entry : mp.entrySet())
        {

            // if prime then increment count
            if (check_prime(entry.getValue())) 
            {
                count++;
            }
        }

        return count;
    }

    // Driver Code
    public static void main(String[] args)
    {
        String s = "geeksforgeeks";

        System.out.println(countPrimeFrequent(s));
    }
}

// This code has been contributed by 29AjayKumar

Python3

# python3 program to find count of numbers 
# with prime frequencies 

# Function to check if a 
# number is prime 

def check_prime(n):
    # Corner cases 
    if (n <= 1): 
        return False 
    if (n <= 3): 
        return True
  
     # This is checked so that we can skip 
     # middle five numbers in below loop 
    if (n % 2 == 0 or n % 3 == 0): 
        return False
  
    for i in range(5,n+1,6): 
        if (n % i == 0 or n % (i + 2) == 0): 
            return False
    return True


# Function to find count of numbers 
# with prime frequencies 
def countPrimeFrequent(s):
    count = 0 
    # create a map to store 
    # frequency of each character 
    mp={} 
  
    # Store frequency of each character 
    # in the mp 
    for i in range(0,len(s)):
        mp.setdefault(s[i],0)
        mp[s[i]]+=1
    
    # now iterate the map and characters 
    # with prime occurrences 
    for i in mp.keys():
        # if prime then increment count 
        if (check_prime(mp[i])):
            count+=1
    return count; 

# Driver Code 
s = "geeksforgeeks" 
print(countPrimeFrequent(s))
# This code is improved by sahilshelangia

// C# program to find count of numbers
// with prime frequencies
using System; 
using System.Collections.Generic;

class GFG
{

    // Function to check if a
    // number is prime
    static Boolean check_prime(int n) 
    {
        // Corner cases
        if (n <= 1)
        {
            return false;
        }
        if (n <= 3)
        {
            return true;
        }

        // This is checked so that we can skip
        // middle five numbers in below loop
        if (n % 2 == 0 || n % 3 == 0)
        {
            return false;
        }

        for (int i = 5; i * i <= n; i = i + 6)
        {
            if (n % i == 0 || n % (i + 2) == 0) 
            {
                return false;
            }
        }

        return true;
    }

    // Function to find count of numbers
    // with prime frequencies
    static int countPrimeFrequent(String s)
    {
        int count = 0;

        // create a map to store
        // frequency of each character
        Dictionary<char, int> mp = new Dictionary<char,int>();

        // Store frequency of each character
        // in the map
        for (int i = 0; i < s.Length; i++)
        {
            if (mp.ContainsKey(s[i]))
            {
                var v = mp[s[i]] + 1;
                mp.Remove(s[i]);
                mp.Add(s[i], v);
            } 
            else
            {
                mp.Add(s[i], 1);
            }
        }

        // now iterate the map and characters
        // with prime occurrences
        foreach(KeyValuePair<char, int> entry in mp)
        {
            // if prime then increment count
            if (check_prime(entry.Value)) 
            {
                count++;         
            }
        }
        return count;
    }

    // Driver Code
    public static void Main(String[] args)
    {
        String s = "geeksforgeeks";

        Console.WriteLine(countPrimeFrequent(s));
    }
}

// This code is contributed by Rajput-Ji

JavaScript

<script>
// Javascript program to find count of numbers
// with prime frequencies


// Function to check if a
// number is prime
function check_prime(n) {
    // Corner cases
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;

    // This is checked so that we can skip
    // middle five numbers in below loop
    if (n % 2 == 0 || n % 3 == 0)
        return false;

    for (let i = 5; i * i <= n; i = i + 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return false;

    return true;
}

// Function to find count of numbers
// with prime frequencies
function countPrimeFrequent(s) {
    let count = 0;

    // create a map to store
    // frequency of each character
    let mp = new Map();

    // Store frequency of each character
    // in the map
    for (let i = 0; i < s.length; i++) {
        if (mp.has(s[i])) {
            mp.set(s[i], mp.get(s[i]) + 1);
        }
        else {
            mp.set(s[i], 1);
        }
    }

    // now iterate the map and characters
    // with prime occurrences
    for (let it of mp) {

        // if prime then increment count
        if (check_prime(it[1]))
            count++;
    }

    return count;
}

// Driver Code

let s = "geeksforgeeks";

document.write(countPrimeFrequent(s));

// This code is contributed by Saurabh Jaiswal
</script>

Output

Time Complexity: O(n + n * sqrt(n)). where n is the length of the string.
Auxiliary Space: O(m). where m is the number of unique characters in the input string.

Array elements with prime frequencies

sahilshelangia

Improve

Article Tags :

Practice Tags :

Array elements with prime frequencies

Similar Reads

Thank You!

What kind of Experience do you want to share?